Signaling interfaces that transmit across long cables between electronic hardware (e.g., low-voltage differential signaling (LVDS)) are susceptible to noise when not actively driven. In some situations, when a signaling interface is inactive (i.e., undriven), noise or cross-talk couples onto the cable of the inactive interface and can make it appear as though the inactive interface is active. When this occurs, the receiver can switch autonomously, causing undesirable results. This problem is particularly present in high-reliability, cross-strapped systems where the primary and redundant driver interfaces are not powered at the same time, but the primary and redundant receivers are powered.
Fail-safe bias resistors have been added to the signal lines in order to keep the input of the receiver at one level and prevent floating due to noise. Typically, these resistors are included in the input of the receiver and are connected to a power supply and ground. For differential signals, the high side is pulled up to the level of the power supply and the low side is pulled down. In some applications, particularly cross-strapped systems, the bias resistors are too weak to overcome the significant noise that may couple onto a long cable. If the resistors are made stronger to compensate for this, often the drivers cannot overcome the biasing current, which can affect the normal operation of the interface when biasing is not needed.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for dynamic fail-safe biasing circuitry for fault-tolerant applications.